Photographic elements relying on silver halide emulsions for image recording are employed in radiographic assemblies. It is known that silver halide emulsions are more responsive to light than to X rays. Accordingly, intensifying screens are used in radiographic assemblies. An intensifying screen contains a phosphor which absorbs X radiation and emits radiation in the visible spectrum or in an adjacent spectral region, ultraviolet or infrared.
It is also desirable to limit patient exposure to high levels of X radiation. Dual coated radiographic assemblies are used to allow reduced levels of X radiation to obtain a useful radiograph. Accordingly, radiographic assemblies can comprise a dual coated light sensitive radiographic element disposed between a pair of fluorescent intensifying screens. The intensifying screens, upon exposure to X radiation, emit radiation in the visible spectrum or in an adjacent spectral region, e.g. ultraviolet or infrared that exposes the silver halide emulsions and results in a recorded image in both emulsion layers.
An image sharpness limitation of dual coated radiographic elements results from a phenomenon known as "corssover". Crossover occurs when light emitted by each intensifying screen passes through the film support, exposing and giving rise to an unsharp image in the oppositely situated silver halide emulsion layer.
A variety of techniques have been tried to reduce crossover. One approach is to dissolve a filter in one or more of the hydrophilic colloid layers or in the support forming the radiographic element. Accordingly, in an ultraviolet light-sensitive radiographic element, an ultraviolet light absorbing compound can be situated between the emulsion layers to reduce crossover of ultraviolet radiation. A desirable characteristic of the ultraviolet light absorbing compound is that it exhibit minimal absorption of light at wavelengths above about 400 nm so that the amount of yellow hue in the radiographic element is thus minimized.
Another approach to improve the clarity of the exposed image by decreasing undesirable yellow hue in a radiographic element is to add a blue dye to the support to offset the yellow, thereby improving the contrast of the exposed image. This approach, however, does not sufficiently offset the yellow hue, and further improvement in decreasing the yellow hue to achieve a sharp image is desirable.
Another prior art approach employs T-Grain.RTM. emulsions to achieve reduction in crossover without emplopying dyes and ultraviolet light absorbers as above. It is desirable, however, to continue to provide an alternative to radiographic elements employing T-Grain ultraviolet light-sensitive emulsions. There is therefore still a need for improved ultraviolet light absorbing compounds for use in non T-Grain, ultraviolet light-sensitive, radiographic elements.
The present invention solves the prior art problems noted above. It provides ultraviolet-light absorption capability sufficient to substantially reduce crossover of ultraviolet radiation to the opposite ultraviolet-sensitive emulsion layer. It achieves a desired level of ultraviolet-light absorption without imparting an undesirable yellow hue to the photographic element. Thus, by means of this invention there is provided a radiographic element that upon exposure to X radiation provides a recorded image substantially free of crossover. The invention thereby provides an exposed image that is sharper and more readable.